This invention relates generally to repeater trunking systems wherein a plurality of mobile or portable radio stations communicate with one another over several communication channels through repeaters operating one each on each of such channels.
This application is related to and an improvement over the system described in commonly assigned copending U.S. patent application Ser. No. 129,645 filed Mar. 12, 1980.
A radio repeater system for a particular geographic locality such as a system used by police, fire, utilities, etc. generally includes multiple repeaters, each operating on one of a plurality of channels assigned for use by that particular repeater trunking system. For example, a repeater trunking system for a local utility company may be assigned channels 1-5. When a mobile user wishes to communicate with one or more other mobile users in a predetermined group, he places his mobile station in a call originate mode, causing it to scan the locally assigned repeater channels to locate a clear channel. Once he finds a clear channel, channel 3, for example, he transmits a signal known as "busy" signal to the repeater operating on that channel. The repeater, upon detecting this busy signal, transmits an acquisition signal having different characteristics from those of the busy signal. This acquisition signal is detected by the mobile user. After this positive "handshake" of signals between a call originating mobile station and a repeater, the repeater and its associated channel become dedicated to the use of the call originating mobile station until it has finished its communication.
Mobile stations utilizing crystals or synthesizers are generally capable of operation on many more channels, i.e., channels 1-25, than are assigned to a particular repeater trunking system in a particular geographic locality. Therefore, before being placed in service, mobile radios are customized for use in a particular service in a particular locality, i.e., their synthesizers are programmed to scan only the channels assigned to a specific repeater trunking system operating in the geographic locality within which it is located. If the mobile station is crystal controlled, they are supplied with crystals allowing operation only on the assigned channels.
It is desirable that mobile users tied to a local repeater trunking system be able to interface with a repeater trunking system operating in a neighboring community. However, using a mobile station that has been customized to operate on five local channels, 1-5, for example, it would be impossible for a mobile user to drive to a different locality and to interface with a repeater trunking system established by a corresponding service, such as a local utility or the local police department in a neighboring community operating on channels 10-15, without reprogramming his mobile radio or substituting appropriate crystals. Such reprogramming is much too complex to be carried out effectively in the field.
One approach to the problem of interfacing with neighboring repeater trunking systems is to dedicate a channel common to all systems. However, this approach requires the use of a computer-based channel transfer arrangement for communications occurring on the common dedicated channel.
In order to allow a direct interface between a mobile user and a neighboring repeater trunking system, it is necessary for his mobile station to be able to operate on the channels of the neighboring system as well as on the channels of his own. However, if each mobile station were equipped to operate on, for example, 25 different channels, so as to be able to interface with neighboring repeater trunking systems, considerable time would be wasted in scanning locally unused channels each time a call were originated.